Before the Ascension, why did the mists appear just as the Well was gaining power? Did they come out at other times?
This one is trickier. From what I got out of it, it’s because the mists are a manifestaion of Preservation, and physical manifestations of Preservation (including Allomancers) are intended to do two things - stop Ruin, and protect the Well of Ascension. Which are kind of the same thing. So, when the Well was dormant, the mists didn’t really have much to do. The Deepness form of the mists is a result of the conscious part of Preservation freaking out and trying to produce a way to protect the well, mostly by producing more Allomancers. That’s why the mists do all the funky things in the Well of Ascension and Hero of Ages - they’re trying to produce more Allomancers to combat Ruin.
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